There is a lot of misleading information on what sparkplugs to use in different applications, or how we dial in spark plugs to a certain application. This thread will be for discussing different configurations and plug reccommendations. So if you have questions or would like some knowledge about the topic please ask for it here. Below is a general outline of what we at NGK reccommend. If you need further assistance please call our tech line at 1-877-473-6767 extension #2.


General reccommendations:

Heat range Static Compression

4 9:1 or less
5 9:1-10:1
6 10:1-10.9:1
7 11:1-11:9
8 12.1:1-13.5:1
9 13.5:1-15.00:1
10 15.5:1-17:1

First we base the heat of the static compression, not dynamic. This will give us a base heat range, then if there are power adders that is where we adjust.

Nitrous

8 Cyl = General rule is one range cooler for every 100 horsepower. I would reccommend one stage cooler for anything up to 125hp. If going further to a 150-225 shot we would need to go cooler and non-projected style plug ( this will lessen the chance of the ground electrode from over heating and melting and causing serious piston damage). For a 250-325 shot go three steps cooler and non-projected.

6 Cyl = A range cooler for up to a 75 shot. A 100-150 shot will be two colder and non-projected. A 175-250 shot would be three cooler and non-projected.


4 Cyl = One cooler for up to a 50 shot. 75 shot to 125 would require a 2 step cooler and non-projected. A 150-225 shot would require 3 cooler and non-projected.


Boost


-- For every 10 psi we reccommend dropping a heat range cooler
-- For 25-30 psi we would reccommend non-projected to prevent blow out
-- For 30 psi and above we would need to go non-projected and a low angle ground electrode or possibly surface discharge.

Keep in mind that we cannot find the correct heat range if some of this data is unknown